Control Flow Messaging ¶

Exercise 5.1 ¶

| divisors |
divisors := [:x | (1 to: x) select: [:d | x \\ d = 0] ].
divisors value: 60.
⇒ #(1 2 3 4 5 6 10 12 15 20 30 60)
divisors value: 45
⇒ #(1 3 5 9 15 45)

Exercise 5.2 ¶

Check the implementations in Boolean, True and False.

Exercise 5.3 ¶

Once the method is edited and saved, in the Method pane select its name teleport: then do ...right click → more... → change category... → events...

Exercise 5.4 ¶

In the Method pane, select one uncategorized control method, then do ...right click → more... → change category → new... key-in control.

To categorized the remaining uncategorized control methods, repeat but select control at the last step as this category now exists.

Exercise 5.5 ¶

We do not need an iterator to detect a collision between two ships. However we use an iterator to take action on each ship when a collision is detected.

SpaceWar>>collisionsShips
| positionA position B |
   positionA := ships first morphPosition.
   positionB := ships second  morphPosition.
   (positionA dist: positionB) < 25 ifTrue: [
      ships do: [:each |
         each flashWith: Color red.
         self teleport: each]
   ]

Local variables only used to ease the code source formatting in printed book.

Exercise 5.6 ¶

You just need to pick the appropriate code snippets from the referenced exercise and examples.

SpaceWar>>collisionsTorpedoesStar
| position |
   position := centralStar morphPosition.
   torpedoes do: [:each | 
      (each morphPosition dist: position) < 8 ifTrue: [
         each flashWith: Color orange.
         self destroyTorpedo: each]]